fix: sanitize page-provided tool strings before they reach model context

[serhiizghama]

Problem

Fixes #2242.

When list_3p_developer_tools runs, McpResponse.getToolGroups() collects tool groups from page JavaScript via the devtoolstooldiscovery event. The name/description of each group and tool are page-provided strings, and they are interpolated directly into the response text the model reads with no sanitization beyond a typeof === 'string' check.

A page being browsed can respond with strings containing:

• newlines — to inject a fake ## System section into the structured response,
• C0/C1 control characters, or
• Unicode bidirectional overrides — to reorder/obfuscate text in the model's context.

This is gated behind categoryExperimentalThirdParty, but for any user who has enabled that category, a visited page can inject content into the LLM context.

Solution

Add sanitizePageString() and apply it to group.name, group.description, tool.name, and tool.description in getToolGroups(), in the Node-side loop that already runs after the values cross the Puppeteer boundary (in-page code is untrusted, so sanitizing there rather than inside evaluate() is deliberate). It:

• strips C0/C1 control characters and Unicode bidirectional formatting characters (U+200E/200F, U+202A–202E, U+2066–2069), and
• collapses any remaining whitespace (newlines, tabs, line/paragraph separators) to single spaces, then trims.

Sanitizing at the boundary means both the rendered text and structuredContent.thirdPartyDeveloperTools are clean, so the fix covers every downstream consumer.

Testing

Added a test in tests/tools/thirdPartyDeveloper.test.ts that has a page respond with a tool group whose strings contain a right-to-left override, a control character, and a newline-led ## System block, then asserts those characters are removed and the injected section is collapsed onto a single line in both structuredContent and the response text. Verified it fails on main and passes with the fix; the existing third-party and McpResponse suites stay green.